Floor underlayment



FIG. 1 is a perspective view of a floor underlayment showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a right elevation view thereof, which is identical to the left elevation view, the front elevation view, and the back elevation view; and,

FIG. 4 is a bottom plan view thereof.

The broken lines show portions of the floor underlayment which form no part of the claimed design. 

CLAIM The ornamental design for a floor underlayment, as shown and described. 